systemd Developer Lennart Poettering lennart@poettering.net sd_id128_randomize 3 sd_id128_randomize sd_id128_get_machine sd_id128_get_boot Generate or retrieve 128 bit IDs #include <systemd/sd-id128.h> int sd_id128_randomize sd_id128_t* ret int sd_id128_get_machine sd_id128_t* ret int sd_id128_get_boot sd_id128_t* ret sd_id128_randomize() generates a new randomized 128 bit ID and returns it in ret. Every invocation returns a new randomly generated ID. This uses the /dev/urandom kernel random number generator. sd_id128_get_machine() returns the machine ID of the executing host. This reads and parses the machine-id5 file. This function caches the machine ID internally to make retrieving the machine ID a cheap operation. sd_id128_get_boot() returns the boot ID of the executing kernel. This reads and parses the /proc/sys/kernel/random/boot_id file exposed by the kernel. It is randomly generated early at boot and is unique for every running kernel instance. See random4 for more information. This function also internally caches the returned ID to make this call a cheap operation. Note that sd_id128_randomize() and sd_id128_get_boot() always return a UUID v4 compatible ID. sd_id128_get_machine() will also return a UUID v4 compatible ID on new installations, but might not on older. It is possible to convert the machine ID into an UUID v4 compatible one. For more information see machine-id5. For more information about the sd_id128_t type see sd-id1287. journalctl1's --new-id command may be used as command line front-end for sd_id128_randomize(). The three calls return 0 on success (in which case ret is filled in), or a negative errno-style error code. The sd_id128_randomize(), sd_id128_get_machine() and sd_id128_get_boot() interfaces are available as shared library, which can be compiled and linked to with the libsystemd-id128 pkg-config1 file. systemd1, sd-id1287, machine-id5, random4